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Appendix II.

on the up stroke as in the Cornish cycle, p. 628, thus dividing the
temperature drop in each cylinder on a semi-compound principle.
Some air being caught in H on the up stroke, serves as a cushion
compelling none but compression stresses on the crank, thus
avoiding the reversal knock and unnecessary alteration of. steam
distribution. The piston and gland rings are all steam packed.
The advantages of such single-acting high-speed engines are (i)
balance due to opposite cranks, (2) economy of the Cornish cycle
or 'transfer system/ (3) constant direction of stress, (4) less
cylinder condensation, and jackets unnecessary, (5) more regular

q 656.

turning effort due to high speed, (6) direct adaptation to dynamo
driving, (7) lighter engine for given power.

The Parsons Steam Turbine is best introduced by a
reading of the matter on water turbines in Chap. XL The first
steam turbine had parallel flow, and was virtually an impulse
machine where the wheel travelled at 40 % of the steam velocity;
the latter being 380 ft per second, and the former making 9000
revs, per m. Per H.P. hour 42 Ibs of steam was used, entering at
84 and leaving at 15 Ibs. absolute pressure. The present motor
has often outward or inward flow, and by compounding or causing
•the steam to pass successively through five or seven wheels, the